The present invention relates generally to a lock mechanism of the type designed to prevent a gliding or hinged door or window from being opened. More particularly, the invention relates to such a mechanism which employs a two piece cam gear/cam rack assembly which both actuates the lock and prevents it from being backdriven.
U.S. patent application Ser. No. 689,296, filed on Apr. 22, 1991 (now U.S. Pat. No. 5,092,640, issued Mar. 3, 1992) and assigned to the same assignee as the present invention, discloses a latch mechanism which is particularly useful in combination with the lock mechanism of the present invention. To the extent that the disclosure of Ser. No. 689,296 is necessary for the understanding of the present invention, that application is herein incorporated by reference.
Various devices are known for locking a gliding or hinged door or window. A common and simple version of such a device has a housing attached to the window frame and a bolt slidably mounted within the housing. A keeper attached to the window sash is positioned to receive the bolt when the window is closed. Thus, the bolt can be moved from a retracted position, where the window can be opened, to a forward position, where the bolt engages the keeper and prevents the window from being opened.
In order to increase the force applied to the bolt so as to make it easier to move the bolt, it is known to provide a rotating actuator for the bolt. The actuator is rotatably mounted on the lock housing, and has at least one arm projecting therefrom. When the actuator is rotated, the arm engages the bolt, causing the bolt to slide into engagement with the keeper. An example of such a window lock is shown in U.S. Pat. No. 800,043 issued to White.
For security purposes, it is important when designing such a window or door lock that the lock cannot be back-driven. In other words, when the bolt is in the engaged position, it should not be able to be forced back into the retracted position by pressure against the bolt. One known lock mechanism which is designed so that it cannot be back-driven is shown in FIG. 1.
As shown in FIG. 1, the lock mechanism has a housing 80 which is designed to attach to one panel of a door or window (not shown). A base member 82 is slidably mounted within the housing. A bolt (not shown) is attached to the base member and positioned to engage a keeper (not shown) located on the door or window frame. An actuator 83 is rotatably mounted on the housing. The actuator is hingedly connected to the base member via arm 84 and link 85.
Rotation of the actuator in the clockwise direction causes the base member (and the bolt attached thereto) to slide linearly into the locked position. In this position, the linkage formed by arm 84 and link 85 is positioned over-center. By this arrangement, the lock mechanism cannot be back-driven, because any attempt to force the base member toward the unlocked position merely causes arm 84 to press harder against stop surface 86.
This lock suffers from several drawbacks. One, the linkage between the actuator and bolt is expensive to manufacture and assemble. The linkage also increases the size of the lock, because room must be provided for both the actuator arm and the link, and because enough space must be provided to allow the linkage to move over-center.